The life and times of M coupe LC61037 and tales of interest for all Z3 M coupe nuts

19 August 2016

Refreshing the Air Conditioning HVAC A/C AC

The AC stopped
working in the car.It had worked sort of OK when I bought it, but it pretty much went to no cooling shortly after Schuh
Syndikat.One way to fix this would be
to just add Freon and hope for the best.But, the car is 18 years old at this point and it’s not getting any
younger.And, I wanted to learn how to
do the work anyway.I chose to replace
the common failure parts.Buying
carefully-picked aftermarket ones, and this service isn’t too expensive.I think pros would charge a FORTUNE for this
sort of work but it really isn’t too hard.I had the center console out anyway and that made it easier.The parts I chose look identical to OEM BMW
ones, and it many cases, they were exactly identical.The one clue I did physically see that was probably a leak in my system was the
hose between the compressor and the condenser was wet with PAG compressor
oil.That is/was the likely leak for me.

I replaced every single o-ring in the
system.I replaced the evaporator, and I
did have to bend the input and output tubes to match the shape of the original
evaporator.I did that using a very wide
gauge screwdriver, inserted into the tubes.And I bent them very slow and carefully.I did replace the OEM foam around the evaporator with new, closed-cell
foam.I figure someone put that there
for a reason, so I replicated it.

The connections at
the firewall between the double pipe (which is inside the cabin) and the hoses,
were tough.BMW uses a steel locating
pin inside the flanged connection to help locate the hoses and line up the
o-rings.But, the double pipe and the hardlines in the engine bay are
aluminum.2 dissimilar metals means
galvanic corrosion.I used a long thin
flat head screwdriver as a chisel to break the connection loose.There is not a lot of room there.

I did notice that several
of the connections had not just an o-ring, but also a small plastic fitting
that snapped onto the end of the male parts of the tubes.I made sure not to lose any of these and I put them all back in place.You need to take great care with this mod to
line up every connection, make sure the o-rings don’t get pinched or roll, and
hand start every bolt.This is not easy
to do!Access is poor in most cases.

I did lube all
o-rings with PAG 100 compressor oil.I
did add 1.5 ounces of PAG oil because I replaced the expansion valve, the
drier, the evaporator, and one line.TIS
shows how much oil to add depending on what you replace.

I did have very bad
luck with the Harbor Freight AC manifold gauge set I used.I failed the leak-down vacuum test many
times, and after I gave up and just decided to add R143A with UV dye,
discovered the failed leak-down test was because the Harbor Freight low
pressure side hose was leaking.I got a
new unit from HF, but it seems to leak too depending on hose orientation.You get what you pay for, and this tool was
only $59.In hindsight, you need a
quality manifold tool with o-ring seals.The HF tool has semi-hard clear plastic washers to make the seals.Not OK.A better way to go would be to spend $159 and get a Snap-On AC manifold
with o-ring seals. I think I got the correct weight of freon into the car, but there is a chance the manifold tool leaked some and I am a little low. Chances are some month when I have $159 burning a hole in my pocket I will get another, proper manifold tool and reload the freon so I can sleep better. The AC is quite cold right now however.

Special thanks to Brent Williams and the Brent Williams Vocational School of Florida for teaching me some basics and some tricks necessary to do this work.

Old evaporator, removed from car. Delicious bits from 17 years of service.

Connection to the double-pipe at the firewall. Note the steel locating pins.

Comparison of old versus new expansion valve. The part numbers show different, but they are physically identical and substitutes for one another according to FCP Euro.

New versus old evaporator cores. Note the orientation of the expansion valves is different. I had to bend the tubing on the new one to match the old unit.

I did find compressor oil (wetness) on the hose between the condenser and the compressor. I replaced this hose, which retails for $157 from BMW with an identical part that did not come in a BMW box for $9 from FCP Euro.

Hose part number

Hose comparison. Not sure if the numbers are dates for the rubber. Seems like they might be.

New drier

Leak in the manifold tool at the low pressure connection. Fantastic.

Another leak in the manifold tool

When adding freon, you can put the cans into a warm water bath. This will help the freon boil off and make its way into the system.

Freon fill specs.

This is how much I theoretically put into my system after vacuuming it out. But, I think I actually have less than this because even the second manifold seemed to leak a little.

Weighing the freon before and after.

Ambient conditions in my garage at time of filling

After freon filled.

Evaporator and expansion valve sealed back into the airbox in the cabin. I used metal HVAC tape over closed cell foam to replicate the seal the factory used.